[PATCH] New option --enable-pie-programs

[Fangrui Song]

On 2021-11-18, H.J. Lu via Libc-alpha wrote:
>On Thu, Nov 18, 2021 at 10:09 AM Siddhesh Poyarekar <siddhesh@gotplt.org> wrote:
>>
>> On 11/18/21 23:28, H.J. Lu wrote:
>> >> How do you see --disable-default-pie behaving with a compiler that
>> >> produces PIE by default?  That is, in case where
>> >> libc_cv_cc_default_pie=yes?  Should it add -fno-pie or leave it as is?
>> >>
>> >
>> > It should add -fno-pie by default when building programs.
>> >
>>
>> In that case I'm inclined towards --enable-default-pie=yes being the new
>> default since AFAIK at least Ubuntu will have to start adding
>> --enable-default-pie to its flags to maintain its current state with its
>> default-pie toolchain.  With Fedora too I think we'd prefer to build PIE
>> by default and I suspect other distros would be OK with that too.
>>
>> Those that don't could add --disable-default-pie to continue maintaining
>> status quo.  This is a step forward security-wise IMO.
>>
>
>Sounds reasonable to me.

As a bonus, --enable-default-pie matches the GCC configure option name:)

As of the auto mode which adds neither -fno-pic nor -fpie, I think it is
unnecessary. --enable-default-pie + --disable-default-pie are sufficient.

---

I think --enable-default-pie is the majority in the Linux world, so
perhaps someone may want to make it the default in the upstream GCC.

After one or two llvm-project releases, I'll adjust my Clang patch
https://reviews.llvm.org/D113372 to default to PIE.